1. Field of the Invention
The invention relates to a planetary roller speed changer and an assembly method and a mounting method for the planetary roller speed changer, and in particular, to a unit that reduces irregularity of rotation of an output shaft.
2. Description of the Related Art
For a sheet feeding mechanism for a printer or a copier (hereinafter referred to as a “printer or the like”), a feeding speed needs to be precisely controlled in order to improve printing quality. The feeding mechanism is driven by a motor 105 to change the speed of rotation transmitted from the motor to transmit the changed speed. In this case, a planetary roller speed changer 100 is used which allows rotary motion of the motor 105 to be precisely transmitted. As depicted in FIG. 7, in the planetary roller speed changer 100, a plurality of planetary rollers 103 is arranged between a fixed ring 101 and a sun shaft 102 that are arranged coaxially with each other. Revolving motion of the planetary rollers 103 in conjunction with rotation of the sun shaft 102 is output as rotation of a carrier 107 (Japanese Patent Application Publication No. 2015-113931 (JP 2015-113931 A)).
In the planetary roller speed changer 100, if the revolution center of the planetary rollers 103 is misaligned with the rotation center of the carrier 107, the revolution angle of the planetary rollers 103 deviates from the rotation angle of the carrier 107. Thus, even when the sun shaft 102 is rotated at a constant speed and the planetary rollers 103 revolve at a constant speed, the carrier 107 rotates at a varying speed. In this case, accurate transmission of rotation of the motor 105 to the output shaft 108 fails, resulting in a displaced printing position and thus degraded printing quality. Thus, for the printer or the like, coaxiality between the pitch circle center of the planetary rollers 103 and the rotation center of the carrier 107 needs to be approximately 10 μm. “Rotation irregularity” is a phenomenon in which the rotation speed or angle of the output shaft 108 increases or decreases with respect to the rotation speed or angle of the sun shaft 102, which serves as an input shaft.
When the planetary roller speed changer 100 is mounted to the printer or the like (not depicted in the drawings), positioning pins 110 are installed on a mounting surface of the planetary roller speed changer 100 and are fitted into respective pin insertion holes formed in the printer or the like for alignment. However, to allow the planetary roller speed changer 100 to be easily assembled to the printer or the like, a clearance is formed between each of the positioning pins 110 and a corresponding one of the pin insertion holes in the printer or the like when the pins 110 are fitted into the respective holes. Thus, the mounting position of the planetary roller speed changer 100 may be slightly displaced. As a result, the output shaft 108 of the planetary roller speed changer 100 may be misaligned with the input shaft of the printer or the like.
If the above-described misalignment occurs, the output shaft 108 is displaced according to the position of the input shaft of the printer or the like. As a result, the output shaft 108 comes into contact with a deep groove ball bearing and is thus tilted, misaligning the rotation center of the carrier 107 and the revolution center of the planetary rollers 103. This disadvantageously leads to the rotation irregularity.